Three Bad Components Found In Power Adapter
Power supply repair and a good lesson to learn
A customer who owns a store nearby brought a power supply for repair. There was no sign of life in it, it was completely dead.
It is a China made power supply but it was the original one that came with the printer when he first bought it.
This is the layout of the power supply and the first thing I checked was the fuse.
It was blown and that means something is wrong in the nearby components such as bridge rectifier, capacitor or the main Mosfet.
It is a 3.15 amp fuse. I roughly checked the surround components but strangely nothing was shorted out. I did not like the sound of that so instead of putting a new fuse, I added a light bulb to the main connection of the fuse and powered it up.
And as expected, the light bulb was shinny bright indicating a short somewhere and that did not make sense.
I decided to take every component off board and test and hope for the best. the first thing I came across was the bridge rectifier and this time it showed two way reading across the AC and the ( -) side on that part.
The second component I came across was the main capacitor. It tested fine before but now it was testing only 1.7 UF out of 68 UF and that was really bad.
Because of the work load I was getting in the shop that week, I was not doing things the way it should be when it comes to testing. I want it done the fast way so I can fix everything in no time and that is a lesson to be learned here. Never ever rush through when it comes to testing and repairing electronics.
Anyway, I replaced all these bad components and before I added the fuse I checked with the light bulb trick once again to make sure.
This time, the light bulb stayed dim and the LED light of the power supply was on as well. Now it was safe to replace the fuse and get it over with.
Mission Accomplished.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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Note: You can check his previous repair articles in the link below:
https://jestineyong.com/shorted-transistors-in-active-sound-speakers/
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Parasuraman S
June 2, 2020 at 9:34 am
A very good article especially with the following advice:
'I want it done the fast way so I can fix everything in no time and that is a lesson to be learned here. Never ever rush through when it comes to testing and repairing electronics.'
That is very true!
Waleed Rishmawi
June 2, 2020 at 8:04 pm
Parasuraman: I thank you my friend. have a blessed day
josé roberto nogueira
June 2, 2020 at 12:40 pm
Very good work. Thank so much.
Regads,
Roberto Nogueira
Waleed Rishmawi
June 2, 2020 at 8:04 pm
Jose: you are most welcome. have a blessed day
Albert van Bemmelen
June 2, 2020 at 12:52 pm
Time is always of the Essence they say, but as long it constitutes no breach in any contract we better take enough time to rule out problems that arise from hasty repairs. And another phrase says it is always better to be safe than sorry. Why I always tell my shopowner friend not to handle any repairs while customers are waiting in his store. They can wait at home too and this way secure the repair is done safely.
Waleed Rishmawi
June 2, 2020 at 8:05 pm
Albert: well said my friend. have a blessed day
Tayo
June 2, 2020 at 7:15 pm
Thank you Waleed for this article. Wise advise but since you do this for a trade you were right to take the easy way first before going through the laboriously steps of taking all the components off the board for individual testing. But i am curious about the capacitor and how it read good the first time. Did you test it in circuit or something?
Waleed Rishmawi
June 3, 2020 at 3:14 pm
Taya: it actually wasted my time taking the easy way out, I should have done it the right way at first.
about the capacitor. after I got the power supply fixed, I tried to power the machine with it, it did not work. the power was flickering on the power supply LEd light. so I tested further and the capacitor was really bad. I did not suspect any wrong with that capacitor till I actually powered on the device.
Pothuwilage Don Lakshman
June 5, 2020 at 12:22 pm
Thank you a lot for sharing your experience with all of us. It was really of good use to me as a technician .